Modern techniques used by hearing instrument manufacturers for obtaining a person's ear canal geometry utilize highly-compliant polymeric materials that are injected into the canal with a syringe. After the material cures, it is pulled from the ear thereby giving a three dimensional impression of the ear canal geometry. Traditionally, the impression is cast in a silicone investment and removed, thereby leaving a representation of the original ear canal. In a procedure that is similar to the traditional casting of a bell, a custom earmold is created by pouring resins into the investment and allowing them to cure into plastic. Although this technique gives a reasonably accurate representation of the ear canal geometry, it does not yield any mathematical information about its shape.
Most hearing instrument manufacturers have adopted laser scanning of traditional impressions as the method of obtaining mathematical representations of the ear canal geometry. A dispenser will acquire the impression from the patient and mail the impression directly to the manufacturer. Unfortunately, the impression can become distorted during the mailing process due to uncured material and excessive temperatures in the delivery trucks; the result is an inaccurate impression of the patient's physiology thereby leading to a hearing instrument that does not fit properly. It is common practice for the dispenser to acquire another impression from the patient and return the hearing instrument for rework.
In some instances, it is common for the hearing instrument to pop out of the patient's ear during chewing or other jaw motion. Since the impression is obtained in a “static” condition within the ear canal, geometry changes of the ear canal during chewing can cause the hearing instrument to jostle and pop out. In order to mitigate these occurrences, it may be advantageous to acquire two different impressions: one with the jaw closed and one with the jaw open. The final earmold for the hearing instrument can be extrapolated as an average from the two impressions, thereby reducing the potential for “popout”.
Depending on the cure rate of the polymeric material used for ear impressions, the process can typically take from ten to fifteen minutes per pair of impressions, not to mention administrative time in preparing, shipping, and receiving the impressions. Recently, laser technology has been used to scan the features of the impression into a mathematical format such as “point cloud” data. These data are used to create a custom shell with automated, digital shell making processes. Unfortunately, the inconvenience of taking a person's ear impression remains the first step in this procedure.
There is a need in the art for a better way to characterize the geometry of a person's ear canal. It would be advantageous to have a process that acquires a representation of the geometry of the ear canal in less time. It would be further advantageous to be able to forward data of the representation directly to a manufacturer to save shipping time and cost.